The present invention relates generally to calibration and verification of a measurement instrument and, more particularly, to a system and method for calibrating and verifying a photometric semen quality analyzer.
Over the past two decades, most animals have experienced a reduction in overall fertility. This decline in fertility among animals has been attributed to many factors, including pollution and global warming. Subfertility in males can usually be identified by taking a sperm count, which requires magnification to increase the apparent size of the microscopic sperm cells so that they can be quantified by a human or by computer. The microscopic cells are studied to determine the total number of cells per unit of volume, the degree of motility and the general shape of the cells. The overwhelmingly most important fertility measurement, however, is the concentration of motile sperm cells that are capable of impregnating an egg. Prior art techniques for measuring fertility include Computer Assisted Semen Analysis (CASA), general microscopy, biochemical assays and the use of a Sperm Quality Analyzer (SQA).
An SQA is a computerized device used by sperm banks, fertility clinics and laboratories to measure certain characteristics of sperm. During use, a sperm sample is drawn into a transparent capillary with precise internal dimensions. After the sample rises into the capillary, the carrier is inserted into an elongated slot wherein a calibrated light is directed by a fiberoptic conduit to illuminate a small segment of the capillary. A photosensor senses the occurrence and frequency of minute perturbations caused by movement of the sperm cells in the light passing through the capillary. The perturbations are converted into digital data and communicated to a computer, which applies a known algorithm to the data and produces a numerically expressed Sperm Motility Index (SMI) that reflects overall sperm quality or relative fertility of the sperm samples. The SMI is also referred to as the Sperm Quality Index (SQI).
For precise fertility measurements over time, an SQA requires repeated calibration to ensure the fidelity of the fiberoptic conduit. In addition, SQAs are often calibrated against other SQAs in an effort to limit instrument-to-instrument variation. For these reasons, there is a need for a high precision SQA calibration system that utilizes uniform measurement standards in order to reduce instrument-to-instrument variation.
In one embodiment of the present invention, a system for calibrating a sample analysis instrument is provided. The system comprises an optical shutter that is inserted into an optical chamber within the sample analysis instrument, and a playback circuit coupled to the optical shutter that stores pre-recorded sample waveforms and applies the pre-recorded waveforms to the optical shutter to produce contrast variations in the optical shutter that mimic the random motion of live samples.
In another embodiment of the present invention, a method for calibrating an instrument for analyzing biological samples is provided. The method includes the followings steps:
generating a standard waveform that mimics the known waveform of a particular biological sample;
storing the waveform in a playback circuit; and
applying the waveform to an optical shutter that is inserted into the instrument in order to produce contrast variations in the optical shutter that mimic the random motion of live samples.
In a further embodiment of the present invention, a method for calibrating an SQA instrument for analyzing biological samples is provided. The method comprises the following steps:
placing a waveform playback unit, a reference SQA and an SQA to be calibrated adjacent each other;
generating a periodic waveform with the playback unit that is in the bandpass of the input spectrum of the reference SQA;
inserting an optical shutter of the playback unit into an optical chamber of the reference SQ and adjusting the gain of the playback unit until a mid range amplitude is obtained;
transferring the optical shutter from the reference SQA optical chamber to an optical chamber of the SQA to be calibrated;
adjusting baseline lamp intensity DAC values of the SQA to be calibrated to match those of the reference SQA; and
storing the adjusted lamp intensity DAC values in a memory in the SQA to be calibrated.
Objects and advantages of the present invention include any of the foregoing, singly or in combination. Further objects and advantages will be apparent to those of ordinary skill in the art, or will be set forth in the following disclosure.